Liquid-Crystal Medium for Polymer Sustained Alignment Displays
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Solution Overview
Problem
Current liquid crystal (LC) media for polymer sustained alignment (PSA) displays face issues such as inadequate tilt angles, voltage holding ratio (VHR) limitations, residual unpolymerized reactive mesogens causing image sticking and mura, high viscosity, and stability concerns, especially under UV exposure and contact with black matrix materials.
Innovation Solution
A liquid crystal medium with negative dielectric anisotropy comprising a polymerizable component and a host mixture containing specific compounds of formula A, which enables quick and complete polymerization, stable pretilt angles, reduced viscosity, and high VHR, even under UV exposure, while minimizing residual unpolymerized materials and mura.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional liquid crystal media with reactive mesogens are used in PSA displays, then polymer stabilization can be achieved, but residual unpolymerized reactive mesogens cause image sticking and mura defects
Solution Approach 1:
The patent modifies the chemical structure of reactive mesogens by introducing specific compounds with formula (I) containing cyano groups and aromatic rings. This structural parameter change enhances polymerization completeness and reduces residual monomers, thereby eliminating image sticking and mura while maintaining display stability
Solution Approach 2:
The patent creates a composite liquid crystal medium combining multiple components: conventional liquid crystal compounds, specifically designed reactive mesogens with formula (I), and UV photoinitiators. This composite formulation achieves complete polymerization without residual harmful substances, resolving the contradiction between stabilization and defect prevention
2Stability of the object's composition
If polymerization is performed to stabilize alignment in PSA displays, then pretilt angle stability is improved, but response time increases due to polymer network formation
Solution Approach 1:
The patent introduces specific reactive mesogen compounds with formula (I) that have optimized molecular structures with cyano groups and aromatic rings. These compounds provide localized polymerization characteristics that stabilize pretilt angles while maintaining fast response times through controlled polymer network formation
Solution Approach 2:
The patent changes the chemical parameters of reactive mesogens by using compounds with specific structural features (formula I with cyano and aromatic groups). This parameter optimization enables the polymer network to provide alignment stability without excessive viscosity increase, thus maintaining fast response times
3Stability of the object's composition
If standard reactive mesogens are used for polymerization, then alignment stabilization is achieved, but viscosity remains high affecting switching performance
Solution Approach 1:
The patent modifies the chemical structure of reactive mesogens by introducing compounds with formula (I) containing cyano groups and aromatic rings. This structural parameter change reduces molecular interactions and viscosity while maintaining polymerization capability for alignment stabilization
Solution Approach 2:
The patent uses specifically designed reactive mesogen compounds with localized functional groups (cyano and aromatic structures in formula I). These local structural features reduce overall molecular viscosity while providing sufficient polymerization sites for alignment stabilization
4Speed
If UV photopolymerization is used to generate pretilt angle, then switching performance is improved, but incomplete polymerization leaves residual reactive mesogens
Solution Approach 1:
The patent changes the chemical parameters of reactive mesogens by using compounds with formula (I) that have enhanced UV absorption characteristics and polymerization reactivity. This parameter optimization ensures complete polymerization under UV exposure, eliminating residual reactive mesogens while maintaining fast switching performance
Solution Approach 2:
The patent introduces UV photoinitiators as intermediary substances that facilitate complete polymerization of the specially designed reactive mesogens. These photoinitiators mediate the UV light energy transfer to the reactive mesogens, ensuring complete polymerization and eliminating residual monomers while maintaining switching performance
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution achieves fast response times, low threshold voltages, high birefringence, and improved display reliability with reduced image sticking and mura, maintaining high VHR and stability across various conditions.
Implementation Method 1
The polymerisation of the RMs preferably takes place with an applied voltage in the case of PS-VA and PS-OCB displays, and with or without, preferably without, an applied voltage in the case of PS-IPS displays
Implementation Method 2
A liquid crystal (LC) medium with negative dielectric anisotropy comprising a polymerisable component and a host mixture
Implementation Method 3
high birefringence, and improved display reliability
Data Source
AI summary
The present invention relates to a liquid crystal (LC) medium comprising a polymerisable compound, to a process for its preparation, to its use for optical, electro-optical and electronic purposes, in particular in LC displays, especially in an LC display of the polymer sustained alignment (PSA) type, and to an LC display, especially a PSA display, comprising it.